From: Sarah Sharp [mailto:sarah.a.sharp@xxxxxxxxxxxxxxx] Sent: Wednesday, October 17, 2012 12:09 PM > On Wed, Oct 17, 2012 at 06:49:14PM +0000, Paul Zimmerman wrote: > > From: linux-usb-owner@xxxxxxxxxxxxxxx [mailto:linux-usb-owner@xxxxxxxxxxxxxxx] On Behalf Of Pratyush Anand > > Sent: Wednesday, October 17, 2012 6:13 AM > > > > > > I was trying to test max bulk through put capability of my usb3.0 > > > device. Bulk IN EP Companion descriptor's bMaxburst is 15 in my gadget. > > > My host controller is TUSB7340. > > > > > > I see, that Device Sends ERDY with NumP=16. > > > Host sends ACK with NumP=4. I noticed that xhci driver programs Max > > > Burst Size same as that of reported by companion descriptor. So, what > > > does it mean, host controller's Max Burst is 4 only? So, even if driver > > > programs 15, it is limited by 3. > > > > > > If yes, Does anybody know about any host controller supporting Max Burst > > > as 16 on Bulk EP? > > > > The NumP=4 from the host probably means that the host only has buffer > > space for 4 1K packets. 4K is the page size, so maybe the host was given a > > scatter-gather list made up of single pages (just a guess). Or else the host > > system just cannot empty the buffers quick enough to keep up. > > The SCSI layer and mass storage driver usually queues a scatter-gather > list of 4K entries for the data phase. The Linux xHCI driver turns each > sg-list entry into one TRB, and chains them all into one TD. So it's up > to the host controller to fetch multiple TRBs and set the NumP field > appropriately. > > It's possible the host controller only wants to fetch the current TRB's > worth of data. We could attempt to collasce adjacent sg-list entries, > but I would have to look into whether that's possible, or if the upper > layer is already doing that when it creates the sg-list. > > > What is the host OS and driver? We have found that the Linux xHCI driver > > does not perform very well compared to the MCCI xHCI driver under > > Windows (which AFAIK is the xHCI driver you usually get when you buy a > > NEC/Renesas host adapter). Did you get a Windows xHCI driver along with > > your TUSB7340 adapter? > > Yep, the Linux xHCI driver performance needs improvement. That's next > on my todo list after I slog through my current bug list. Hi Sarah, Actually, I think I misspoke. I suspect it's actually the USB mass-storage class driver, or the layers above it, that is responsible for the slowness. The performance under Windows is comparable to Linux, until you replace the standard USB mass-storage class driver with the one from MCCI (in addition to their xHCI driver). And AFAIK you don't get that driver when you buy a NEC/Renesas add-in card. Which reminds me, I need to do a performance test under Windows 8, to see how it compares using its built-in USB 3.0 support. -- Paul -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
